Catalysts (A-level only)

Transition metals and their compounds can act as heterogeneous and homogeneous catalysts.

A heterogeneous catalyst is in a different phase from the reactants and the reaction occurs at active sites on the surface.

The use of a support medium to maximise the surface area of a heterogeneous catalyst and minimise the cost.

V₂O₅ acts as a heterogeneous catalyst in the Contact process.

Fe is used as a heterogeneous catalyst in the Haber process.

Heterogeneous catalysts can become poisoned by impurities that block the active sites and consequently have reduced efficiency; this has a cost implication.

A homogeneous catalyst is in the same phase as the reactants.

When catalysts and reactants are in the same phase, the reaction proceeds through an intermediate species.

Students should be able to:

• explain the importance of variable oxidation states in catalysis

• explain, with the aid of equations, how V₂O₅ acts as a catalyst in the Contact process

• explain, with the aid of equations, how Fe²⁺ ions catalyse the reaction between I⁻ and S₂O₈²⁻

• explain, with the aid of equations, how Mn²⁺ ions autocatalyse the reaction between C₂O₄²⁻ and MnO₄⁻